1. Field of the Invention
The present invention relates generally to emissions control systems, and more particularly to a control system for the active adaptive control of exhaust gas recirculation and spark advance for an internal combustion engine automobile.
2. Background and Summary of the Invention
The tailpipe exhaust gas of internal combustion engine automobiles generally contains various environmental pollutants such as carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NO.sub.x). In order to reduce the levels of these pollutants, exhaust emission controls in the form of systems, devices, and strategies have been incorporated into most modern automobile designs. These controls work together to reduce the level of pollutants in the exhaust gas emitted from the tailpipe.
Increasing the combustion temperature improves combustion and reduces HC emissions. However, the higher combustion temperature also produces more NO.sub.x. For example, when peak combustion temperature generally exceeds 2500.degree. F. (1372.degree. C.), the nitrogen in the air mixes with oxygen to produce NO.sub.x. This problem has led to the development of the exhaust gas recirculation system, or EGR system.
The EGR system recirculates a small metered amount (typically 6 to 13 percent) of the hot inert exhaust gases back into the intake manifold. The relatively cooler exhaust gas absorbs heat from the relatively much hotter combustion process. This reduces peak combustion temperature and lowers the formation of NO.sub.x.
The EGR system includes a passage between the exhaust manifold and the intake manifold. The EGR valve opens and closes this passage. Thus, the amount of exhaust gas that is recirculated to the intake manifold is controlled by the EGR valve. Such EGR valves can be designed to carefully admit controlled amounts of exhaust gases into the intake manifold. The exact amount required will vary according to several factors, including engine speed and loading. Most modem automobiles employ EGR valves that are operated electronically, typically with the use of a solenoid. A type of EGR valve, known as a linear solenoid EGR valve, allows for a continuously linear variable orifice between the exhaust gas and the intake gas on an internal combustion engine.
Other methods of reducing pollutant levels involves a number of systems that have been developed to alter ignition spark advance to meet most engine operating conditions. One of these methods is spark advance control.
Spark advance causes the spark plug to fire earlier by altering the ignition timing by advancing the distributor or by firing the coil earlier. Typically, the spark plug is fired when the piston is one or more degrees below the top dead center (TDC) position in the cylinder. Most of these systems retard the operation of the vacuum advance unit, when used, or use the engine computer to modify the timing.
Since the introduction of computer engine controls, ignition timing has been precisely controlled by the engine computer. Modern systems use a spark control computer and a number of engine sensors to provide instantaneous timing control. This permits smooth engine operation on diluted fuel-air mixtures.
Although the advent of EGR systems and spark advance control systems have aided in the reduction of pollutants, the lack of precise control and coordination between the two systems has not permitted the attainment of optimal fuel economy with a corresponding acceptable level of emissions control.
Therefore, there exists a need for a system for optimizing the fuel economy of an internal combustion engine automobile by carefully and continuously controlling and coordinating the operation of the EGR system and the spark advance control system.
Accordingly, the present invention provides a control system for the active adaptive control of exhaust gas recirculation and spark advance for an internal combustion engine automobile. While the automobile is operating, a control algorithm continuously receives data input from various sources such as the driving mode monitor, fuel consumption monitor, engine roughness monitor, and the knock system monitor. Based on the data, the control algorithm then causes either an EGR command, a spark advance command, both an EGR and spark advance command, or no command at all to be generated so as to optimize the fuel economy of the automobile. This process is repeated until there is no further beneficial effect on fuel economy or unacceptable levels of engine roughness and/or engine knock are detected.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.